The present invention relates to a circuit arrangement for generating light- and temperature-dependent signals representing properties of an object or a scene. The invention also relates to an imaging pyrometer comprising such a circuit arrangement.
EP 1 134 565 B1 describes an imaging pyrometer which can be used to determine surface temperature distributions of objects in a scene. In addition, this known pyrometer supplies a “normal” optical image of the scene. This is achieved by virtue of the known pyrometer having an optoelectronic sensor comprising a plurality of sensor elements, which are referred to as pixels in the document. The optoelectronic sensor has three different types of sensor elements, which are arranged on the surface of the sensor in an alternating fashion. A first type of sensor elements is designed to generate electrical signals dependent on electromagnetic radiation originating from a very narrowband wavelength range around 1.06 μm. A second type of sensor elements is designed to generate electrical signals dependent on electromagnetic radiation from a second narrowband wavelength range around 0.99 μm. The two narrowband wavelength ranges each contain a small part of the infrared spectrum. A third type of sensor elements is designed to generate electrical signals dependent on electromagnetic radiation from a relatively broadband wavelength range comprising substantially only visible light. The electrical signals from the two infrared ranges are used to determine temperatures according to an algorithm such as is described in U.S. Pat. No. 4,413,324 for example. This involves a quotient method, in which a quotient of the signals from the two narrowband infrared ranges is formed in order to eliminate the emission properties of the surface whose temperature is determined. Merely the “normal” optical image of the observed scene is generated by means of the third electrical signals from the wavelength range of visible light.
The known sensor therefore has three different types of sensor elements, which have to be produced in at least partly different process steps and which have to be distributed on the surface of the sensor. Consequently, the production of the known sensor is rather complicated and expensive. On the other hand, the resolution of the known sensor is limited both with regard to the visual image and with regard to the temperature distribution because the different sensor elements are arranged side by side on the surface of the sensor, such that between two sensor elements of the same type there are in each case “gaps” occupied by sensor elements of a different type. The limited resolution is disadvantageous if one would like to determine geometrical properties of a recorded object on the basis of the optical image, for example. Finally, the dynamic range of the sensor elements is also limited in the case of the known sensor, such that several different exposure times may be required depending on the temperatures and radiation intensities in the observed scene. Consequently, the image recording can be cumbersome.
U.S. Pat. No. 4,413,324, already cited above, discloses a quotient pyrometer comprising a plurality of sensor elements which record electromagnetic radiation in two different wavelength ranges, which are narrowband in each case. The known pyrometer allows to determine a temperature distribution, but it does not allow to record a “normal” optical image of the observed scene.
Furthermore, quotient pyrometers have been known for many years from various documents. By way of example, reference is made to DE 12 37 804 A1, which proposes to determine a logarithm of the measured values at first and to calculate a difference between the logarithms thereafter, with the difference corresponding to the logarithm of the quotient. Said document proposes recording electromagnetic radiation from the red and from the blue wavelength ranges. A similar proposal is found in DE 867 453, wherein electromagnetic radiation from the red and from the green wavelength ranges are to be recorded.
DE 24 27 892 A1 discloses a quotient pyrometer, where the actual temperature in a scene is determined by means of a separate temperature radiator, which provides a reference value for the temperature determination.
DE 11 36 135 A discloses a quotient pyrometer, where a photoelement made of silicon is arranged upstream of a germanium diode in the direction of radiation. The silicon acts as a filter element and allows to pass through predominantly only radiation having a wavelength of greater than 1.2 μm. The germanium diode has a maximum sensitivity in the wavelength range around 1.5 μm. The maximum sensitivity of the photoelement of silicon is approximately 0.9 μm. The temperature in the observed scene is determined from the signals of the two sensor elements.
DE 33 17 108 A1 discloses a thin-film semiconductor component used as a solar cell, for instance. The thin-film semiconductor component is constructed in a layered fashion on a semiconductor substrate.
DE 196 50 705 A1 discloses a camera comprising a plurality of sensor elements arranged one above another in a stacked fashion. By way of example, a color matrix sensor and a black-and-white matrix sensor are arranged vertically one above the other and aligned pixel by pixel with one another. The pn junctions—stacked in the depth—of the sensors react to different wavelengths since the longer the wavelength, the more deeply optical wavelengths penetrate into the material.
Finally, DE 42 09 536 A1 discloses an image cell for an image recorder chip, where a photodiode and a MOS transistor are connected to one another in such a way that charge carriers generated in the photodiode flow away through the channel of the MOS transistor. The MOS transistor is operated in what is called sub-threshold range, which has the consequence that the electrical output signal of the image cell is logarithmically dependent on the intensity of the impinging radiation. This known image cell therefore allows to record highly dynamic light signals. Image recorder chips having this technology are commercially offered by the present applicant under the trade name HDRC®.